Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Statistical Power”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23Linked to original sources
PubMed1996

Meta-analysis of the literature on Alcoholics Anonymous: sample and study characteristics moderate findings.

OBJECTIVE: Reviews of research on Alcoholics Anonymous (AA) have speculated how findings may differ when grouped by client and study characteristics. A meta-analytic review by Emrick et al. in 1993 provided empirical support for this concern but did not explore its implications. This review divided results of AA affiliation and outcome research by sample origin and global rating of study quality. The review also examined the statistical power of studies on AA. METHOD: Meta-analytic procedures were used to summarize the findings of 74 studies that examined AA affiliation and outcome. Results were divided by whether samples were drawn from outpatient or inpatient settings and a global rating of study quality that jointly considered use of subject selection and assignment, reliability of measurement and corroboration of self-report. Efficacy of dividing study results was examined by changes in magnitude of correlations and unexplained variance. RESULTS: AA participation and drinking outcomes were more strongly related in outpatient samples, and better designed studies were more likely to report positive psychosocial outcomes related to AA attendance. In general, AA studies lacked sufficient statistical power to detect relationships of interest. CONCLUSIONS: AA experiences and outcomes are heterogeneous, and it makes little sense to seek omnibus profiles of AA affiliates or outcomes. Well-designed studies with large outpatient samples may afford the best opportunity to detect predictors and effects of AA involvement.

Alcoholics Anonymous↗
PubMed1991

Ticlopidine treatment for patients with unstable angina at rest. A further analysis of the study of ticlopidine in unstable angina. Studio della Ticlopidina nell'Angina Instabile Group.

Data collected to investigate the effects of ticlopidine in a subset of 489 patients with angina at rest accompanied by transient ischaemic electrocardiographic changes have been analysed. Of the 489 patients, 255 received conventional treatment including beta-blockers, nitrates, or calcium antagonists (control group); 234 received conventional treatment plus ticlopidine 250 mg b.i.d. (ticlopidine group). The predefined end-points were vascular death and acute myocardial infarction (AMI). The incidence of end-points was assessed according to the intention-to-treat principle. The post-hoc estimated statistical power was 80%. The rate of death or AMI in the 6-month follow-up period was reduced from 14.9 to 6.8% (-54.4%) (odds ratio: 0.42; confidence intervals: 0.22, 0.80). The incidence of fatal or nonfatal AMI was reduced from 12.2 to 4.3% (-65%) (odds ratio: 0.32; confidence intervals: 0.14, 0.70) and of nonfatal AMI from 10.2 to 3.8% (-63%) (odds ratio: 0.35; confidence intervals: 0.15, 0.80). Nineteen patients died; 12 in the control group (4.7%) and seven in the ticlopidine group (83%) (-36%) (odds ratio: 0.62; confidence intervals: 0.21, 1.74); five patients in the control group and only one in the ticlopidine group died of an AMI. The post-hoc estimated statistical power was 80%. However, we cannot draw definitive conclusions about the clinical effect of ticlopidine treatment in the patients with angina at rest accompanied by transient ischaemic electrocardiographic changes because the subgroup analysis was not planned a priori. Nevertheless, this report strongly suggests that such patients can benefit from antiplatelet treatment with ticlopidine; the benefit mainly depends on the protective effect against myocardial infarction.

Aged↗
PubMed2000

State parity legislation and changes in health insurance and perceived access to care among individuals with mental illness: 1996-1998*

BACKGROUND: The 1990's witnessed a new wave of state and federal legislation affecting mental health insurance in the United States. Although patient advocacy groups have hailed the passage of numerous "parity" laws that require insurance coverage for mental illnesses to equal that for physical ailments, it is unclear whether this activity represents a major improvement in insurance benefits among mentally ill or significantly increases their access to care. AIMS: This paper contrasts how insurance coverage has changed among individuals with mental health problems in states with and without parity legislation. METHODS: National survey data from 1996 to 1998, subset to a panel of 1220 individuals exceeding clinical screeners for a mental health disorder. Dependent variables are change in insurance status, insurance generosity and perception of access to care. The analysis contrasts changes in dependent variables between states with and without parity legislation (a difference-in-differences analysis). RESULTS: There are no statistical significant effects of state parity; point estimates suggest that parity mandates are associated with a slightly higher number of mentally ill reporting improved insurance generosity and access to care, but also with a higher number of mentally ill losing all insurance coverage in parity states. The estimated effects are too small to be statistically significant, although the sample size is limited and the study had only good statistical power to detect large effects. DISCUSSION: At the population level, state parity legislation appears to have not had large effects on the insurance coverage of the group that was intended as the primary beneficiary of legislation. Likely reasons include the limited scope of the actual legal requirements and large numbers of mentally ill that are not covered by health insurance subject to such legislation. The results do not exclude the possibility that some subgroups experienced substantial improvements in their insurance coverage. At the population level, large effects experienced by small subgroup are diluted by groups that experienced no similar changes. However, parity legislation was not considered a minor issue by advocates and opponents and this analysis has the statistical power to detect the sizeable differences that were argued in the policy debate. IMPLICATIONS FOR HEALTH POLICIES: While state parity legislation may have improved insurance benefits for some, it appears not to have resulted in substantial improvements for the mentally ill as a whole. The results could be very different, however, if strong federal legislation were passed that has a broader scope than state legislation. IMPLICATIONS FOR RESEARCH: The parity debate provides an important reminder of how little research is available to inform policy. This study provides a crude picture, but it is far from being a conclusive evaluation. The most urgent need is for data that continue to track changes in markets and policies.

Journal Article↗
PubMed2004

Evaluation of vardenafil and sildenafil on cardiac repolarization.

This novel study evaluated the effects of vardenafil and sildenafil on QT and corrected QT (QTc) duration using a model that minimizes experimental error to obtain the most accurate assessment of observed QTc effects. A placebo-controlled and positive-controlled, period-balanced, double-blinded, 6-way crossover study evaluated therapeutic and supratherapeutic oral doses of vardenafil (10 and 80 mg, respectively) and sildenafil (50 and 400 mg, respectively), therapeutic doses of moxifloxacin (400 mg), and a placebo in 58 healthy men (mean age 53 years), with dosing every 3 days. Six replicate, 12-lead, digital electrocardiograms (ECGs) were recorded at 3 time points before and 5 time points after dosing to cover the time course of maximum exposure to study drugs and their metabolites. An independent laboratory blindly analyzed approximately 17,000 ECGs. For the placebo, mean change in QTcF (Fridericia) duration 1 hour after dose (approximate Tmax of vardenafil and sildenafil) was 0 ms (+/-0.7 SD). QT/QTc variability was small across regimens, indicating statistically powerful results. Moxifloxacin demonstrated an expected 8-ms mean change and was the only drug to prolong absolute QT. Placebo-corrected mean changes in QTcF duration (90% confidence interval) at 1 hour after dose were 8 ms (range 6 to 9) for vardenafil 10 mg and 6 ms (range 5 to 8) for sildenafil 50 mg. QTci (linear and nonlinear per patient) yielded similar trends: 4 ms (range 3 to 6) for vardenafil 10 mg and 4 ms (range 2 to 5) for sildenafil 50 mg. Dose response demonstrated very shallow QTc relations for study drugs. Therapeutic and supratherapeutic doses produced only small increases in the QTcF interval, which were considered to be clinically irrelevant. This well-controlled, statistically powerful study in middle-aged men demonstrated that vardenafil and sildenafil produced no increase of absolute QT and only similar, small increases of the QTc interval, with a shallow dose-response curve. The study design and conduct may serve as a guide for future QT assessment of new drugs.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2001

Clinical trials of multiple sclerosis monitored with enhanced MRI: new sample size calculations based on large data sets.

OBJECTIVE: A new parametric simulation procedure based on the negative binomial (NB) model was used to evaluate the sample sizes needed to achieve optimal statistical powers for parallel groups (with (PGB) and without (PG) a baseline correction scan). It was also used for baseline versus treatment (BVT) design clinical trials in relapsing-remitting (RR) and secondary progressive (SP) multiple sclerosis (MS), when using the number of new enhancing lesions seen on monthly MRI of the brain as the measure of outcome. METHODS: MRI data obtained from 120 untreated patients with RRMS selected for the presence of MRI activity at baseline, 66 untreated and unselected patients with RRMS, and 81 untreated and unselected patients with SPMS were fitted using an NB distribution. All these patients were scanned monthly for at least 6 months and were all from the placebo arms of three large scale clinical trials and one natural history study. The statistical powers were calculated for durations of follow up of 3 and 6 months. RESULTS: The frequency of new enhancing lesions in patients with SPMS was lower, but not significantly different, from that seen in unselected patients with RRMS. As expected, enhancement was more frequent in patients with RRMS selected for MRI activity at baseline than in the other two patient groups. As a consequence, the estimated sample sizes needed to detect treatment efficacy in selected patients with RRMS were smaller than those of unselected patients with RRMS and those with SPMS. Baseline correction was also seen to reduce the sample sizes of PG design trials. An increased number of scans reduced the sample sizes needed to perform BVT trials, whereas the gain in power was less evident in PG and PGB trials. CONCLUSION: This study provides reliable estimates of the sample sizes needed to perform MRI monitored clinical trials in the major MS clinical phenotypes, which should be useful for planning future studies.

Adult↗
PubMed2005

Lack of tachyphylaxis to methacholine at 24 h.

OBJECTIVE: To examine for tachyphylaxis to methacholine at 24 h and to use these data to assess the repeatability of the provocative concentration of a substance causing a 20% fall in FEV1 (PC20) for methacholine and to obtain statistical power calculations. DESIGN: Retrospective review of four double-blind, placebo-controlled studies with two methacholine PC20 values measured at 24-h intervals. SETTING: Tertiary university hospital bronchoprovocation laboratory. PATIENTS: Thirty-two subjects with mild-to-moderate well-controlled asthma. INTERVENTIONS: The placebo arms of the four studies were examined. MEASUREMENTS: Methacholine PC20 (using 2-min tidal breathing method) initial determination and repeat testing at 24 h. RESULTS: The geometric mean PC20 values were 1.57 mg/mL (95% confidence interval [CI], 1.0 to 2.4 mg/mL) and 1.62 mg/mL (95% CI, 1.0 to 2.6 mg/mL NSD; p = 0.64). The mean absolute difference between the two measurements was < 0.4 doubling concentrations, and 31 of 32 measurements had both values within one doubling concentration. These data provide a statistical power of 92% for 10 subjects to show a one-half concentration deltaPC20 and a mean power of 99 +/- 1% to show a one-concentration deltaPC20. CONCLUSIONS: There is no evidence for methacholine tachyphylaxis at 24 h in subjects with asthma. At 24 h, the average repeatability was well within a one-half concentration change, and individually 31 of 32 measurements (97%) were within one doubling concentration.

Adolescent↗
PubMed2002

Genetic and molecular analyses of complex metabolic disorders: genetic linkage.

Wide efforts have taken place with complex metabolic disorders to emulate the success that linkage analysis has had in explaining the nature of monogenic metabolic diseases such as MODY (maturity-onset diabetes of the young) and FH (familial hypercholesterolemia). New linkage methods are being specifically developed and tested for complex disorders since some of the basic assumptions of traditional linkage analysis used with Mendelian traits are not valid. The nature of complex diseases precludes the use of extended families under the hypothesis that the same disease allele acts in most affected individuals throughout a pedigree. Rather, a multitude of genes and of rare and common alleles creates an apparently chaotic pattern of heterogeneity within and between families. Therefore, very simple family structures, in many studies even isolated sibling pairs, form the basis of efforts to compare the inheritance of disease with that of the chromosomal regions under investigation. Also, assumptions about how individual loci contribute to the overall disease inheritance used for the models applied in linkage computation have to be kept to a minimum. The overall effect of this, together with the potentially weak influence of many loci, is a heavy toll on the statistical power to detect individual contributing genes. This may be the reason why very few scans so far have yielded disease loci that meet genome-wide significance criteria. The confirmation of original loci in secondary studies has proven, as predicted, to be very difficult. Nevertheless, the overall emerging picture is very encouraging: one of the genome scans in type 2 diabetes has been carried through to the positional cloning of the underlying genetic variant, namely, the calpain 10-associated polymorphism in type 2 diabetes. Several other loci have been detected repeatedly throughout studies in various human racial groups, such as the chromosome 1q and 20q diabetes loci, and have become the target of collaborative fine-mapping efforts. Modifications to present methodology are in development with the goal to increase statistical power: examples are the use of intermediate traits with potentially increased genetic homogeneity, the investigation of admixed populations, and the study of linkage disequilibrium over wide genomic regions.

Diabetes Mellitus, Type 2↗
PubMed1993

Automated morphometric analysis of stallion spermatozoa.

Tissue variation in microscope slides made for spermatozoon analysis and variation introduced by the subjective techniques used to analyze these slides reduce the statistical power of studies that seek to use spermatozoon morphology to predict fertility. A simple specimen preparation method was developed to standardize stallion spermatozoon morphologic smears, and a new, automated spermatozoa morphometry instrument was used to objectively analyze the efficacy of the specimen preparation technique. The method achieved a standard spermatozoon concentration and reduced field-to-field variation in the number of spermatozoa analyzed. Metric measurements of spermatozoon head dimensions from clinically normal, fertile stallions revealed small, but highly significant, differences between stallions. The variation in metric measurements between replicate slides within stallions was small, indicating that replicate slide analysis probably is not necessary for clinically normal stallions. Coefficients of variation were generally < 11% for metric measurements between stallions, and were < 4% within stallions. This study revealed that a high degree of statistical power can be achieved when using these new, standardized specimen preparation and objective analysis techniques. Such power makes possible the detection of subtle differences between clinically normal stallions, and may facilitate accurate detection of abnormal fertility (ie, subfertility) in stallions.

Animals↗
PubMed1993

Estrogen replacement therapy and breast cancer risk.

Assessment of the effects of menopausal estrogens on the risk of breast cancer is obviously complex, with proper evaluations requiring attention to the effects of selection, recall, and surveillance biases; confounding factors; detailed exposure relations; and subgroup variations. Although much discussion has ensued over the extent to which variations between studies might be due to a variety of methodological differences, it is likely that the limited statistical power of many studies may be largely responsible for the divergent effects observed, particularly with regard to assessing the effect of long-term usage. Thus, in case-control studies in which population controls have been used and for which there have been a sufficient number of women using estrogens for approximately 10 or more years, it appears as though such an exposure may be associated with some elevated risk, possibly on the order of 30-80 percent (16, 34, 36-38)--a magnitude of risk that is obviously extremely difficult to detect in most epidemiologic studies. Evaluation of risks associated with short-term use is even more difficult, which has led most investigators to conclude that usage of less than 5 years is associated with no detectable excess risk. Problems with statistical power also plague evaluations of more detailed measures of use, including dosage and type of preparations, although there is some indication that nonconjugated preparations may be associated with a higher risk than other types of estrogens (16, 20, 36, 44, 51). In addition, there is some evidence that recent use may be associated with a modest elevation in risk (32, 33, 53), although effects of surveillance bias are difficult to resolve. Interpretation of the effect is complicated by several studies which have found estrogens to be associated with an increased risk of breast cancer incidence but a decreased risk of death, with the mortality ratios ranging from approximately 0.5 to 0.8 (33, 92, 93). Although one of these studies hypothesized that the relation with mortality may reflect a tendency for women with clinically recognized breast cancers and those at high risk not to be prescribed estrogens for long periods of time, studies showing that estrogen users have more favorable tumor characteristics at diagnosis than nonusers (20, 36) suggest that screening biases may be involved. The numerous contradictions regarding effects of menopausal estrogens from observational studies have heightened interest in the results of several ongoing controlled clinical trials.(ABSTRACT TRUNCATED AT 400 WORDS)

Breast Neoplasms↗
PubMed2003

A randomized trial comparing induction chemotherapy followed by surgery with surgery alone for patients with stage IIIA N2 non-small cell lung cancer (JCOG 9209).

OBJECTIVE: We performed a prospective randomized trial in patients with potentially resectable stage IIIA N2 non-small cell lung cancer to confirm the efficacy of induction chemotherapy before surgical resection. METHODS: Patients with stage IIIA N2 non-small cell lung cancer, all with histologically or cytologically confirmed metastases to the ipsilateral mediastinal lymph nodes, were randomly assigned to receive either three cycles of induction chemotherapy (cisplatin at 80 mg/m(2) on 1 day and vindesine at 3 mg/m(2) on 2 days) followed by surgery or surgery alone. RESULTS: This trial was prematurely terminated because the accrual rate was too slow, which lowered the study's statistical power considerably. From June 1993 through April 1998, a total of 62 patients were enrolled, and 31 patients were assigned to each treatment group. The objective clinical response rate of induction chemotherapy was 28%. Complete resection was achieved in 20 patients in the induction chemotherapy group (65%) and 24 in the surgery alone group (77%). Median follow-up was 6.2 years. Median overall survivals were 17 months for the induction group and 16 months for the surgery alone group. The estimated 1-, 3-, and 5-year survivals, respectively, were 68% (95% confidence interval 51%-85%), 23% (95% confidence interval 8%-38%), and 10% (95% confidence interval 0%-20%) for the induction chemotherapy group and 65% (95% confidence interval 48%-82%), 26% (95% confidence interval 11%-41%), and 22% (95% confidence interval 7%-37%) for the surgery alone group. There was no statistically significant difference in survival between the groups (P =.5274). Treatment-related death was not observed in either group. CONCLUSION: This randomized trial to compare induction chemotherapy (cisplatin and vindesine) followed by surgery with surgery alone for patients with stage IIIA N2 non-small cell lung cancer did not demonstrate a survival difference between the groups, although this may have been because the statistical power was limited.

Adult↗
PubMed1996

Pairwise analysis of radiation hybrid mapping data.

Two point lod scores are widely used in pedigree analysis as they provide a fast and efficient method of establishing linkage. Groups of markers that lie in close proximity to one another can be formed by admitting any locus that is linked to at least one existing member of the group with lod score greater than some predetermined value. It seems natural to extend this technique to Radiation Hybrid Mapping both for constructing groups of tightly linked loci that may then be analysed using more powerful statistics and as a method of ordering in its own right. A general extension of two point analysis is derived and the problems associated with radiation hybrid data are discussed. In particular, the additional parameters representing the probabilities of different fragments being retained (which have no parallel in classical linkage analysis) lead to a range of estimators of the breakage probability, O, which have equal and maximal likelihood. Ways of circumventing this problem are discussed along with the potential errors they introduce. Importantly the ambiguity in estimation of theta is not carried through to the lod score as this depends only on the maximum value of the likelihood and not on the particular value of theta at which it occurs. Thus even though two point analysis fails to provide robust estimates of either breakage probabilities or the distance between loci, it represents a simple and effective method of constructing linkage groups that may be analysed with more powerful statistical methods. This is particularly important given the large number of microsatellites, ESTs and candidate genes currently being typed on radiation hybrids.

Chromosome Mapping↗
PubMed2001

The Norsjö-Cooperstown healthy heart project: a case study combining data from different studies without the use of meta-analysis.

OBJECTIVES: This paper aims to develop and describe a method for combining. comparing, and maximizing the statistical power of two longitudinal studies of risk factors for cardiovascular disease that did not have identical data collection methodologies. METHODS: Subjects from a 1986 cross-sectional study (n = 180) were pair-matched with subjects of corresponding gender and age (+5 years) from a 1990 cross-sectional study. The methodology is described and results are calculated for various measures of cardiovascular risk or risk factors (e.g. cholesterol. Finnish Risk Score). RESULTS: Box's test of equality and symmetry of covariance matrices gave chi-square values of 223.8 and 710.0 for two cardiovascular risk factors (cholesterol and cardiac risk score, respectively); these values were highly significant (p=0.0001) For the North Karelia Risk Score, repeated measures ANOVA revealed a borderline significant interaction for treatment by time (p=0.054) and a significant interaction for treatment by time by country (p=0.035). These probabilities compared favorably with a randomized blocks model. CONCLUSIONS: Creation of a synthetic longitudinal control group resulted in a statistically valid ANOVA model that increased the statistical power of the study.

Adult↗
PubMed2004

Measurement procedures in confocal choroidal laser Doppler flowmetry.

PURPOSE: To estimate a practical number of measurements within a series of recordings with a confocal choroidal laser Doppler flowmeter, capable of providing an adequate statistical power for future studies. METHODS: Ten independent measurements of choroidal blood flow were obtained within 30 minutes in one randomly selected eye of 24 subjects. In 12 subjects, subsequent series of 10 measurements were also obtained 2 and 7 days after baseline assessment. Average and median values of these series were calculated for the choroidal blood flow parameters velocity, volume, and flux, using either the first 3, the first 4, the first 5, the first 6, the first 7, the first 8, the first 9, or all 10 measurements. The variance between the series was analyzed using non-parametric tests. RESULTS: The average values of a series of independent measurements decreased with an increasing number of independent measurements. More than 5-7 independent recordings did not markedly influence the estimate of the average value of choroidal blood flow parameter for an individual. Baseline measurements showed markedly higher values than subsequent series. Average values obtained with 6 independent measurements seem to provide a reasonable level of statistical power for paired comparisons, 13 subjects providing a 80% power at a probability level of 0.05 to find a significant difference of 15% between two means. CONCLUSION: It seems recommendable that experimental measurements with a confocal choroidal laser Doppler flowmeter are preceded by a session of familiarization and that average values of series of at least 6 measurements are used.

Adult↗
PubMed2003

Homeopathy for childhood diarrhea: combined results and metaanalysis from three randomized, controlled clinical trials.

BACKGROUND: Previous studies have shown a positive treatment effect of individualized homeopathic treatment for acute childhood diarrhea, but sample sizes were small and results were just at or near the level of statistical significance. Because all three studies followed the same basic study design, the combined data from these three studies were analyzed to obtain greater statistical power. METHODS: Three double blind clinical trials of diarrhea in 242 children ages 6 months to 5 years were analyzed as 1 group. Children were randomized to receive either an individualized homeopathic medicine or placebo to be taken as a single dose after each unformed stool for 5 days. Parents recorded daily stools on diary cards, and health workers made home visits daily to monitor children. The duration of diarrhea was defined as the time until there were less than 3 unformed stools per day for 2 consecutive days. A metaanalysis of the effect-size difference of the three studies was also conducted. RESULTS: Combined analysis shows a duration of diarrhea of 3.3 days in the homeopathy group compared with 4.1 in the placebo group (P = 0.008). The metaanalysis shows a consistent effect-size difference of approximately 0.66 day (P = 0.008). CONCLUSIONS: The results from these studies confirm that individualized homeopathic treatment decreases the duration of acute childhood diarrhea and suggest that larger sample sizes be used in future homeopathic research to ensure adequate statistical power. Homeopathy should be considered for use as an adjunct to oral rehydration for this illness.

Child, Preschool↗
PubMedDate not supplied

Immunonutrition in clinical practice: what is the current evidence?

The clinical trials of immunonutrition that we have undertaken have often been small, single centre studies. They have often been of limited statistical power and have often included patients with a variety of underlying disease states and at different points in the disease process. Three meta-analysis and a consensus statement in conjunction with a systematic review, have been performed in an attempt to overcome many of these limitations and understand further the clinical place for immunonutrition. However, there are still many questions regarding the place of immunonutrition in clinical practice that we still do not understand or have definitive answers to. For example, do we really know what is the optimal combination of nutrients and in what quantities they should be provided? Do we understand any potential interactions that might occur between these nutrients? What is the effect of the patients nutritional state? When and for how long should immunonutrition provided? What is the impact of the patients' underlying disease process and how does this interact with the provision of immunonutrition? At the present time whilst there is some indication and evidence as to which patients might benefit most, and as to those who may not benefit or even suffer detrimental effects from immunonutrition, we still can not answer these questions with any definitive authority. It is essential now that we undertake large well designed, well controlled multicentre studies with adequate statistical power to answer these questions. The indications are that immunonutrition has the potential to help patients but its place must be more clearly defined before its widespread acceptance into clinical practice is based on sound scientific evidence.

Clinical Trials as Topic↗
PubMed2006

Extent of prostate-specific antigen contamination in the Spanish section of the European Randomized Study of Screening for Prostate Cancer (ERSPC).

OBJECTIVES: The performance of tests outside prostate cancer screening trials (PSA contamination) may affect their statistical power. The present study addressed the extent of PSA contamination in the Spanish section of the European Randomized Study of Screening for Prostate Cancer (ERSPC) and its impact on biopsy performance and prostate cancer detection. METHODS: Data linkage was performed to address screening-related interventions outside the study. Four databases were used: (1) Spanish ERSPC database (n=4278), (2) laboratory database with all PSA determinations (n=31,140), (3) database of 1608 prostate biopsies, and (4) records of all prostate cancers (n=819) diagnosed at our centre. PSA contamination, biopsy performance, and cancer detection rates were calculated. RESULTS: Median follow-up time was 6.6 yr. A total of 2201 PSA determinations were performed for 1253 men. Cumulative PSA contamination was 29.3% (17% in the control arm during the first 4 yr). A higher proportion of men undergoing biopsies was found in the screening arm (21.3% vs. 2.9% in the control arm, p<0.0001). Similarly, higher cancer detection rates were found in the screening (4.7% vs. 1.2% in the control arm, p<0.0001). CONCLUSIONS: In our experience, the PSA contamination rate has increased during the last years, but its impact on biopsy performance and cancer detection in the control arm of the trial is limited and not likely to compromise the statistical power of the ERSPC trial.

Aged↗
PubMed2003

ST-deviation reconstruction in missing leads on the 12-lead ECG: applicability in studies on ST-segment resolution during thrombolysis.

Quantitative analysis of ST-segment deviations (STdev) and their resolution by treatment (STR; calculated from a combined sum of STdev in multiple leads) are used in trials on reperfusion for myocardial infarction (MI). Unreadable or unavailable electrocardiogram (ECG) leads are a common reason for exclusion, decreasing the statistical power of the trials. We developed mathematical formulas for reconstruction of immeasurable STdev based on STdev from other available leads on the 12-lead ECG. Formulas were deducted from a database of computer-assisted STdev measurements in 2 ECGs (baseline and 180 min after thrombolysis) of 1121 pts. Their accuracy was later evaluated on a second dataset of 377 pts. Acceptable fits could be derived for absent single leads, or for groups of absent limb leads (I-II-III or aVL-aVF). The intraclass correlation coefficient between real and calculated STdev was >or= 0.80 for each (0.77 for V1 in inferior MI). The correlations between STR calculated from original data and from reconstructed STdev were very strong (all intraclass correlation >or=0.97), and discordance in STR subgroup categorization occurred in <or=10% of pts in all but one of the scenarios (I-II-III substituted in 180 min ECG in inferior MI). Scenarios with multiple missing precordial leads however are not substitutable, nor are calculated STdev reliable for STR evaluation in only the lead with highest elevation in baseline. STdev reconstruction formulas can reliably be used in trials where analysis of aggregate STR is an endpoint. Reliable substitution can significantly increase the number of evaluable patients and therefore strengthen the statistical power of these trials.

Electrocardiography↗
PubMed1999

Frequency of major adverse cardiac events within one month of coronary angioplasty: a useful measure of operator performance.

OBJECTIVES: To test one-month outcomes in a single center for their statistical power to corroborate conclusions derived from large multicenter databases. BACKGROUND: Only with large, multicenter databases has it been possible to demonstrate more frequent occurrences of complications in patients treated by "low-volume operators." Critics feel that such analyses mask excellent performance by many "low-volume operators." METHODS: In a high-volume cardiac catheterization laboratory in a large, nonuniversity teaching hospital, baseline clinical and angiographic characteristics were collected for a consecutive series of 1,029 patients treated by 37 percutaneous transluminal coronary intervention (PTCI) operators over a four-month period. One-month follow-up was obtained in 967 (94%) patients who form the basis for this analysis. RESULTS: Only the group of operators performing <50 cases annually had a major adverse cardiac event (MACE) (death, myocardial infarction or symptom-driven revascularization) rate at one month significantly greater than predicted from baseline characteristics. (Observed rate: 15.1%, expected: 9.7%, 95% confidence interval [CI]: 4.7%, 14.6%.) The difference was driven by the significantly more frequent rate at which repeat revascularization was performed in patients treated by that group of operators (observed: 13.8%, expected: 7.1%, 95% CI: 2.8%, 11.4%). CONCLUSIONS: As is true of analyses of large multicenter databases, lower volume operators as a group have less good outcomes than those performing more. The greater statistical power provided by one-month MACE rate offers advantages over the use of in-hospital complications for the analysis of operator performance.

Aged↗